1. Field of the Invention
This invention is directed to a system and method for obtaining measurements across the width of a material being dried in an industrial dryer.
2. Description of Related Art
Industrial dryers are used, for example, in drying tobacco in various processed forms prior to the tobacco being used in producing finished products. Other products also require drying as part of the processing to produce the final product. In certain tobacco drying processes, for example, an “apron”, or substantially continuous moving sheet, of tobacco in semi-processed condition is passed through dryer units at one or more stages prior to packaging for shipment to a tobacco products manufacturer. The tobacco is checked for moisture content after it has been processed through the dryer, in order to determine whether the moisture level of the tobacco is at or below the maximum moisture level as dictated by the tobacco products manufacturer. If the moisture level exceeds the maximum level imposed, the tobacco must be reprocessed at great expense to the supplier, in order to be sold to the tobacco products manufacturer.
Similar scenarios are present in a variety of industries outside the area of tobacco production, in which the moisture content or other properties of the intermediary product must meet specifications dictated by the purchaser of the intermediary product. In such instances where moisture content is measured only at the completion of processing, the same situation can arise that the intermediary product must be further processed in order to be accepted by the purchaser.
Moisture control in apron style tobacco dryers has long been a challenge to the industry. This is due to the fact different tobaccos and tobacco blends have varying densities, as well as percentages of casing, affecting the tobacco carpet depth and/or mass flow throughput. The leaf stalk position and the environmental conditions at the time of processing also contribute to changes in the drying process. These changes represent more or less work/energy transfer required to achieve the desired results. This causes the operator to adjust both heating (drying) and re-ordering (moisturizing) zones of this multiple stage process. Most tobacco processing lines have dryers with three or more zones of heating, one or more zones of cooling, and two or more zones of re-ordering.
Processing originally depended entirely on the acquired skill of the operator's hand to determine the approximate moisture content of the tobacco discharging from the dryer. With the reduction of cost for a standard on-line moisture gauge to less than $10K per unit, many dryers are now fitted with moisture gauges at the discharge to assist operators in monitoring the quality of the product exiting the dryer. To date, most operations have relied on this final moisture value supported by lab results, in conjunction with measured internal dryer temperatures, to make necessary adjustments to control the process.
Recently, with the need to achieve the highest production rates possible with existing equipment and ever tightening customer product quality control standards, tobacco processors have been looking for a method to better control the drying process and reduce standard deviation. One major problem has been that the drying process is both multiple zone and bi-directional. Therefore, no reliable means for determining the average moisture after drying and before re-ordering was readily available. Some processors have placed standard on-line moisture gauges inside the cooling sections of dryers with limited success. Mainly because it is a single point-measuring device mounted at a fixed position along the longitudinal axis of an apron style dryer, the data does not provide a true profile of the product across the entire dryer width and therefore is of limited use. This is further complicated by the fact standard photometers (moisture gauges) in this environment are operating near or at their maximum operating temperature, affecting both their performance and life cycle (MTBF).
It is therefore a principal object of the present invention to provide a system and method for taking measurements of, for example, moisture levels present in a moving product stream, and employing that information to aid in determining whether the product will meet moisture level requirements imposed by a purchaser of the product.
It is a further principal object of the present invention to provide a system and method for taking measurements of, for example, moisture levels present in a moving product stream, and employing that information in a control loop or control scheme for controlling process equipment used to produce the desired product.
It is a further principal object to provide a system for measuring particular properties of a material being processed in an enclosed area, which deploys a compact detector head within the enclosed area, and which delivers an NIR reflected energy to an electronics package external to the enclosed area for processing.